1. Field of the Invention.
The present invention relates to an ultrasonic transmitting and receiving system for digital communication by means of using a transmitting device including a piezoelectric substrate and an interdigital transducer (IDT) with a coded pattern, and a receiving device including a piezoelectric substrate and an IDT with a coded pattern in reverse to the IDT in the transmitting device.
2. Description of the Prior Art.
Of late years, digitalization techniques on telegraphic communication are in rapid progress. A code division multiple access (CDMA) method is, more especially, powerful for making a transmission speed high in spread spectrum communication. If a surface acoustic wave (SAW) matched filter is incorporated in the CDMA method, it is possible to make the transmission speed still higher. However, it is difficult for a conventional type of CDMA method with the SAW matched filter to realize a base-band communication because of a coded message-signal in condition of a phase shift keying (PSK) burst-signal. In other words, it is necessary to transduce the PSK burst-signal to a digital pulse signal with a high speed for the base-band communication. In order to make the digital pulse signal, the use of a complicated circuit is unavoidable for the conventional type of CDMA method with the SAW matched filter.
An object of the present invention is to provide an ultrasonic transmitting and receiving system for digital communication comprising a transmitting device and a receiving device.
Another object of the present invention is to provide the transmitting device capable of coding a message digital-signal applied thereto, and delivering a coded digital-signal into a digital network.
Another object of the present invention is to provide the receiving device capable of receiving the coded digital-signal from the digital network, and detecting an output digital-signal corresponding to the message digital-signal.
Another object of the present invention is to provide an ultrasonic transmitting and receiving system for digital communication capable of making the coded digital-signal, in the digital network, play a role as a pseudo noise to keep a base-band communication secret.
Another object of the present invention is to provide the transmitting- and receiving devices capable of recognizing each other in the digital network.
Another object of the present invention is to provide an ultrasonic transmitting and receiving system for digital communication capable of a low electric power consumption.
Another object of the present invention is to provide an ultrasonic transmitting and receiving system for digital communication excellent in durability and manufacturing.
A still other object of the present invention is to provide an ultrasonic transmitting and receiving system for digital communication having a small size which is very light in weight and has a simple structure.
According to one aspect of the present invention there is provided an ultrasonic transmitting and receiving system for digital communication comprising a transmitting device and a receiving device. The transmitting device consists of an input terminal, a first piezoelectric substrate, an input IDT, a first electrode-group, an envelope detecting device, and an output terminal. The receiving device consists of a receiving terminal, a second piezoelectric substrate, a second electrode-group, an intermediary IDT, an output IDT, and a detecting terminal. The input IDT consists of at least three interdigital electrode pairs Pi (i=1, 2, . . . , n), of which two neighbors are at a distance L from each other, and has a coded pattern. The first electrode-group consists of an interdigital electrode A0 and an interdigital electrode Ai (i=1) at a distance iL (i=1) from the interdigital electrode A0. The input IDT and the first electrode-group are formed on the first piezoelectric substrate. The second electrode-group consists of a central interdigital electrode B0, a left interdigital electrode Bxe2x88x921 at a distance L0 from the central interdigital electrode B0, and a right interdigital electrode Bi (i=1) at a distance L0+iL (i=1) from the central interdigital electrode B0. The output IDT has a coded pattern in reverse to the input IDT. The second electrode-group, the intermediary IDT, and the output IDT are formed on the second piezoelectric substrate.
When a pulse (1) of a message digital-signal is applied to the input IDT via the input terminal, a first SAW is excited on the first piezoelectric substrate. And then, a coded burst-signal corresponding to the first SAW is detected at the interdigital electrode A0, and the interdigital electrode Ai after a time corresponding to the distance iL. The use of the envelope detecting device causes a double-coded digital-signal from the coded burst-signal at the interdigital electrode A0 and that at the interdigital electrode Ai. Thus, the double-coded digital-signal is delivered into a digital network via the output terminal. On the other hand, if the double-coded digital-signal is received at the left interdigital electrode Bxe2x88x921 and the right interdigital electrode Bi from the digital network via the receiving terminal, second- and third SAWs are excited on the second piezoelectric substrate, respectively. The second- and third SAWs are transduced to a monocoded burst-signal at the central interdigital electrode B0. When the monocoded burst-signal arrives at the intermediary IDT, a fourth SAW is excited on the second piezoelectric substrate. In this time, if the fourth SAW corresponds to the first SAW, a decoded pulse (1) is detected at the output IDT. Thus, an output digital-signal, which is composed of the decoded pulse (1) and no detected pulse (0), and is equivalent to the message digital-signal, is delivered at the detecting terminal.
According to another aspect of the present invention there are provided input- and output IDTs, of which coded patterns are changed in accordance with a designated time region, respectively.
According to another aspect of the present invention there is provided a transmitting device, wherein a transmitting direction of the second- and third SAWs is orthogonal to that of the fourth SAW.
According to another aspect of the present invention there are provided; a first electrode-group including at least two interdigital electrodes Ai {i=1, 2, . . . , (nxe2x88x921)} at a distance iL {i=1, 2, . . . , (nxe2x88x921)}, respectively, from the interdigital electrode A0; and a second electrode-group including at least two right interdigital electrodes Bi {i=1, 2, . . . , (nxe2x88x921)} at a distance L0 +iL {i=1, 2, . . . , (nxe2x88x921)}, respectively, from the central interdigital electrode B0. In such arrangements, the interdigital electrodes Ai take turns in connecting with the envelope detecting device, and at the same time, the at right interdigital electrodes Bi take turns in connecting with the receiving terminal.
According to another aspect of the present invention there are provided first- and second piezoelectric substrates made of a piezoelectric ceramic, respectively, the polarization axis thereof being parallel to the thickness direction thereof.
According to another aspect of the present invention there are provided first- and second input IDTs in place of the input IDT, and first- and second output IDTs in place of the output IDT. The first input IDT consists of at least three interdigital electrode pairs Pi (i=1, 2, . . . , n), of which two neighbors are at a distance L from each other, and has one coded pattern. The second input IDT consists of at least three interdigital electrode pairs Pi (i=1, 2, . . . , n), of which two neighbors are at a distance L from each other, and has the other coded pattern. The first output IDT has a coded pattern in reverse to the first input IDT. The second output IDT has a coded pattern in reverse to the second input IDT.
When pulses (0and 1) of a message digital-signal are applied to the first-and second input IDTs, respectively, via the input terminal, first- and second SAWs are excited on the first piezoelectric substrate. And then, a coded burst-signal corresponding to the first- and second SAWs, respectively, is detected at the interdigital electrode A0, and the interdigital electrode Ai after a time corresponding to the distance iL. Thus, a double-coded digital-signal is detected at the envelope detecting device from the coded burst-signal at the interdigital electrode A0 and that at the interdigital electrode Ai, and delivered into a digital network via the output terminal. On the other hand, if the double-coded digital-signal is received at the left interdigital electrode Bxe2x88x921and the right interdigital electrode Bi from the digital network via the receiving terminal, third- and fourth SAWs are excited on the second piezoelectric substrate, respectively. The third- and fourth SAWs are transduced to a monocoded burst-signal at the central interdigital electrode B0. When the monocoded burst-signal arrives at the intermediary IDT, a fifth SAW is excited on the second piezoelectric substrate. In this time, if the fifth SAW corresponds to the first- and second SAWs, respectively, decoded pulses (0 and 1) are detected at the first- and second output IDTs, respectively. Thus, an output digital-signal, which is based on the decoded pulses (0 and 1) and is equivalent to the message digital-signal, is delivered at the detecting terminal.
According to other aspect of the present invention there are provided first-and second input IDTs, of which each coded pattern is changed in accordance with a designated time region, and in the same time, first- and second output IDTs, of which each coded pattern is changed in accordance with a designated time region.
According to a further aspect of the present invention there is provided an input IDT in place of the first- and second input IDTs. The input IDT has two coded patterns, which are exchanged from each other in response to the pulses (0 and 1) of the message digital-signal applied to the input IDT.